Effects of histone modifications on structure of higher order chromatin have been studied; Hl phosphorylation apparently loosens the structure somewhat, this is reflected in melting temperature and sedimentation behavior. Salt gradient dialysis experiments have shown that nucleosome placement can occur at any site on SV-40 DNA; no sequence can not be folded by histones. Micrococcal nuclease and DNAase I both excise the receptor for triiodothyronine (T3) from chromatin early in digestion as a 6S sedimenting species. With higher digestion, the sedimentation coefficient decreases to 5S, still greater than the free receptor at 3.5S. We suggest that the receptor is associated with DNA and an extended nucleoprotein in the 6S primary product. Yeast RNA polymerase II has been isolated and purified to greater than 80% purity. The enzyme transcribes core particles at a rate half that of their constituent protein-free DNA. Surprisingly, about 4 polymerase molecules can bind to either core particles or their DNA and crosslinked core particles are transcribed as readily as native nucleosomes.